Cosimo di Giovanni de' Medici (September 27, 1389 – August 1, 1464), was the first of the Medici political dynasty, de facto rulers of Florence during most of the Italian Renaissance; also known as "Cosimo 'the Elder'" ("il Vecchio") and "Cosimo Pater Patriae."
In 1433 Cosimo's power over Florence, which he exerted without occupying public office, began to look like a menace to the anti-Medici party, led by figures such as Palla Strozzi and Rinaldo degli Albizzi: in September of that year he was imprisoned, accused for the failure of the conquest of Lucca, but he managed to turn the jail term into one of exile. He went to Padua and then to Venice, taking his bank along with him. His brother Lorenzo joined him after a failed attempt to raise an army to conquer the city by force. Prompted by his influence and his money, others followed him: within a year, the flight of capital from Florence was so great that the ban of exile had to be lifted, making Cosimo return a year later in 1434, to greatly influence the government of Florence (especially through the Pitti and Soderini families) and to lead by example for the rest of his long life.
Cosimo's time in exile instilled in him the need to quash the factionalism that resulted in his exile in the first place. In order to do this, Cosimo, with the help of favourable priors in the Signoria, instigated a series of constitutional changes to secure his power through influence.
In the political sphere, Cosimo worked to create peace in Northern Italy through the creation of a balance of power between Florence, Naples, Venice and Milan during the wars in Lombardy, and discouraging outside powers (notably the French and the Holy Roman Empire) from interfering. In 1439 he was also instrumental in convincing pope Eugene IV to move the Ecumenical council of Ferrara to Florence. The arrival of figures from the Byzantine Empire, including Emperor John VIII Palaiologos himself, started the boom of culture and arts in the city.
Cosimo was also noted for his patronage of culture and the arts, liberally spending the family fortune (which his astute business sense considerably increased) to enrich Florence. According to Salviati's Zibaldone, Cosimo stated:
He also hired the young Michelozzo Michelozzi to create what is today perhaps the prototypical Florentine palazzo, the austere and magnificent Palazzo Medici. He was a patron and confidante of Fra Angelico, Fra Filippo Lippi, Michelangelo and Donatello, whose famed David and Judith Slaying Holofernes were Medici commissions. His patronage enabled the eccentric and bankrupt architect Brunelleschi to complete the dome of Santa Maria del Fiore, and the dome was perhaps his crowning achievement as sponsor.
In the realm of philosophy, Cosimo, influenced by the lectures of Gemistus Plethon, established a modern Platonic Academy in Florence. He appointed Marsilio Ficino as head of the Academy and commissioned Ficino's Latin translation of the complete works of Plato (the first ever complete translation). Through Ficino and others associated with the Academy, Cosimo had an inestimable effect on Renaissance intellectual life.
On his death in 1464 at Careggi, Cosimo was succeeded by his son Piero 'the Gouty', father of Lorenzo the Magnificent. After his death the Signoria awarded him the title Pater Patriae, "Father of his Country", an honor once awarded to Cicero, and had it carved upon his tomb in the Church of San Lorenzo.
Cosimo also had an illegitimate son by a Circassian slave; Carlo (c. 1428 - 1492) became a prelate.